Hypertension is a common manifestation of renal disease and greatly contributes to its progression as well as to cardiovascular morbidity. Clearly, hypertension is an important etiology in the pathogenesis of renal failure. In the United States, hypertension is the primary cause of end-stage renal disease in approximately 29 percent of dialysis patients. In conjunction with other diseases such as diabetes and chronic glomerulonephritides, hypertension, when uncontrolled, hastens the progression of renal disease. Cardiovascular disease is the leading cause of death in patients receiving maintenance hemodialysis and hypertension is considered the most important factor responsible for cardiovascular events in these patients. Adequate BP control may reduce the progression of renal disease and cardiovascular morbidity in these patients, but often this is difficult to achieve with currently available drugs. The old paradigm is that hypertension in renal disease is the result of activation of the renin-angiotensin system and/or volume expansion. Our studies strongly support the notion that a renal injury may result in activation of renal afferent pathways that integrate with the central nervous system, and lead to stimulation of efferent SNS activity and hypertension. Locally produced angiotensin II in the brain in response to these afferent stimuli seems to be responsible for SNS activation through inhibition of nitric oxide. Our hypothesis is that angiotensin-II activation of ROS may reduce NO availability in key brain region and result in increased SNS activity in a model of neurogenic hypertension caused by renal injury developed in our laboratory. To test this hypothesis we will pursue 3 specific Aims: 1. Test the hypothesis that locally produced Ang II mediates the activation of central SNS activity caused by phenol-renal injury. To this end, we will measure Ang II concentration in the dialysate collected from the PH using the microdialysis technique, and the expression of renin mRNA in the posterior hypothalamus. 2. Test the hypothesis that radical oxygen species (ROS) activated by Angiotensin II down-regulate nitric oxide production in the brain resulting in increased SNS activity. To this end, we will measure the concentration of reactive oxygen species (ROS) in the hypothalamus or rats with the phenol-renal injury or rats infused with Ang II in the lateral ventricle. In addition, we will evaluate the effects of anti-oxidants, or scavengers of ROS, and Ang II AT1 receptor antagonists on BP, sympathetic activation and ROS concentrations in the hypothalamic region. 3. Test the hypothesis that increased ROS production may result in NO inhibition and SNS activation in other forms of experimental hypertension, such as the DOCA-sait model, and the renovascular hypertension model. If our hypothesis were to be correct, administration of inhibitors of the renin-angiotensin system particularly if combined with antioxidants should result in better control of BP in these models.